Conventionally a rolling bearing for use in engines of automobiles, motorcycles, and the like and particularly a needle roller bearing having a cage is frequently used by silver-plating the surface of the cage to prevent the surface thereof from seizure. The cage of the needle roller bearing is produced by stamping and the cage retains needle rollers at regular intervals. The entire surface of the cage produced by stamping is silver-plated. As a method of surface-treating the cage, a barrel plating method of performing plating treatment by immersing an object in a plating solution with the object accommodated inside a barrel in which electrodes are disposed and electrically conducting the object, while the plating solution is being stirred is known.
FIG. 11 shows the outline of the barrel plating method. FIG. 11 is a flow diagram of the barrel electroplating method.
The barrel electroplating method is carried out in the steps of cleaning—ground plating—cleaning—main plating—cleaning and drying with an object to be plated accommodated in a barrel. The cleaning step includes degreasing cleaning, acid cleaning, and water cleaning. At the time of the main plating, to improve the quality of plating, strike plating is often used in combination with the barrel electroplating method.
According to the barrel electroplating method, it is possible to simultaneously plate a plurality of fine objects difficult to be plated by directly mounting an electrode thereon and objects having different sizes. Therefore the barrel plating method is frequently used for the cage for the rolling bearing.
As a barrel plating apparatus, to improve defective conduction of an electricity-feeding portion, there are disclosed-a plating apparatus (see patent document 1) having a construction which allows the electricity-feeding portion to be conductive by supporting an electricity-feeding shaft by an electricity-feeding bearing device and a plating apparatus (see patent document 2) capable of allowing a plating-tank and a barrel to be electrically conductive by merely placing the barrel on the plating tank.
The service conditions, where the silver plated, cage for the rolling bearing is used, have become more severe than conventional service conditions. Thus the improvement of the durability of the cage in a sliding operation is required.